High voltage oil insulated and cooled armature windings

ABSTRACT

The armature of a high-voltage electrical generator or motor is contained in a chamber which also contains transformer oil or other suitable insulating and cooling fluid. The oil immerses the armature winding and provides protection against corona and flashover. The oil is also circulated through the chamber and along, across and over the armature conductors including if desired associated structure such as a magnetic shield to provide cooling of the conductors and structure. An oil pump and oil cooler external to the chamber provide a closed oil circulating system.

United States Patent [191 11] 3,743,867 Smith, Jr. July 3, 1973 [54]HIGH VOLTAGE ()IL INSULATED AND 3,242,418 3/1966 Mela ..l 3l0/40 COOLEDARMATURE WINDINGS 3,368,087 2/1968 Madsen 3l0/52 [75] Inventor: JosephL. Smith, Jr., Concord, Mass. I Primary Examiner Rl Skudy [73] Assignee:Massachusetts Institute of Attorney-Martin M. Santa et al.

Technology, Cambridge, Mass. [22] Filed: Dec. 20, 1971 [57] ABSTRACT[2!] Appl. No.: 210,088 The armature of a high-voltage electricalgenerator or motor is contained in a chamber which also contains 52 us.CI. 310/52, 310/86 *F table fluld. The Oil immerses the armature windingand pro- [51] Int. Cl. H02k 9/00 vldes protection against corona andflashover. The Oil [58] Field of Search 310/52, 40, 64, 85, l l d h h hh b d l W86 54 53 58 55 1s a so CII'CU ate t roug t e c am er an aongacross and over the armature conductors including if desired associatedstructure such as a magnetic shield [56] References Cited to providecooling of the conductors and structure. An UNITED STATES PATENTS oilpump and oil cooler external to the chamber pro- 3,5l7,23l 6/1970 Massar310/86 vide a closed oil circulating system, 3,657,580 4/1972 Doyle310/52 3,644,766 2/1972 Hughes 310/40 10 Claims, 2 Drawing Figures HIGHVOLTAGE OIL INSULATED AND COOLED ARMATURE WINDINGS This inventionrelates to improving the high voltage insulation of the armature windingof large electrical machines while at the same time providing adequatecooling. This invention is especially applicable to extremelyhigh-voltage machines with superconducting field windings.

In large conventional synchronous machines the armature winding isinsulated with plastic, glass and mica flake insulation. Cooling isprovided by direct liquid cooling of the stator conductors in theselarge highvoltage generators. Water is usually employed as the coolingmedium and is circulated down the length of the armature conductor andis confined within the armature conductor by connections which are madeat both ends of the armature conductor through insulated tubes. Thewater is used solely for the function of cooling. The voltage of thearmature conductors appears across the tubing at the ends of thearmature.

Since hydrogen most effectively cools the rotor and the stator iron,with a minimum windage loss, large generators employ a hydrogenatmosphere which also provides additional cooling from the exterior ofthe armature conductor. Thus, it is necessary to mechanically isolatethe water supply in the interior of the conductor from the hydrogen gason the exterior of the conductor. This form of construction does notovercome the problem produced by charging of the insulation by inductionwhich results in corona loss and the possibility of flashover throughthe hydrogen to the surrounding iron frame.

The problem of corona discharge will be increased in the more recentdesigns of electrical machines where output voltage of the order of I00KV appear practicable as compared with the 30 KV output voltage ofconventional machines. These machines will utilize cryogenic orsuperconducting field windings together with a special winding of thearmature to provide the high voltage. A more detailed discussion of sucha machine is to be found in the doctoral thesis of James F. Kirtley,Jr., Design and Construction of an Armature for an Alternator with aSuperconducting Field Winding, August 1971, a copy of which is in theU.S. Patent Office Scientific Library.

A machine with a superconducting rotor winding will have a rotor designwhich thermally isolates the rotor from the armature winding. Forthermal isolation, an

' evacuated air gap between the rotor and the armature is most desirablesince it provides no windage loss while providing good thermalisolation. Therefore, an air gap fluid, such as hydrogen, is notrequired to provide cooling of the rotor. The rotor and the armature areeach contained within their respective cylindrical enclosures.

This invention provides an armature structure in which oil is used toelectrically insulate the armature winding to reduce the coronadischarge problem in high voltage windings and in addition, to provideintegral cooling by flowing the oil through the armature winding.

The simplest realization of this concept is to contain the armaturewinding in a fluid-tight annular cylindrical tank. Oil is pumped intoone end of this tank, circulates around and through the armatureend-turns, passes longitudinally along, through, and across theconductor bars in the active section of the machine, circulates throughand around the other armature end-turns, and then flows to the other endof the tank where the oil exits. The oil is externally cooled andreturned to the pump suction.

With this oil immersed winding there will be no corona discharges fromthe end-tums where the corona problem is most severe in conventionalmachines. The oil filled cooling passages of the armature conductor barwill not be detrimental to the armature insulation, and the terminalbushings for the machines will be less expensive than the gas-to-gasbushings used in conventional machines.

Other objects and features of this invention will be apparent from thefollowing detailed description of the invention considered inconjunction with the following figures:

FIG. 1 is a lengthwise cross-sectional view of an armature.

FIG. 2 is a cross-sectional view of a segment of the armature.

A cross-sectional view of an electric generator having a superconductingrotor and an armature incorporating this invention is shown in FIG. 1.The armature 1 has its windings 2 circumferentially enclosed by acylindrical tube 3. The interior of the armature 1 comprises a phenolicinner shell 4 in the form of a cylinder. The rotor 5, having asuperconducting field winding 6, cooled by the cryogenic fluid 60 isseparated from the armature winding inner shell 4 by a vacuum space 7.An end flange 8 is attached to the outer tube 3 at each end of thearmature. The flange 8 provides a structure by which the armature may beconnected to a fixed supporting structure by an end bell 9 which issecured to flanges 8 at both ends of the machine. Suitable gasketingmaterial (not shown) is placed between flange 8 and end bell 9 to form aliquid tight seal. The end bell 9 and the inner tube 4 also have agasketed liquid tight seal at each end of the armature. Consequently,the armature winding is contained within a cylindrical chamber 10 whichis capable of containing a fluid under pressure.

The armature outer shell 3 also forms the inner surface of an outercylindrical chamber 11. The outer surface 12 of chamber 11 is analuminum cylinder which provides an eddy current shield to prevent thefield from the superconducting rotor 5 from escaping to the exterior ofthe machine. End closures 13 are connected and gasketed to outer surface12 and flanges 8 to form the liquid tight chamber 11. A removable ironshield 14 may be contained with this chamber 11 as an alternate form ofapparatus for confining the rotor flux within the machine.

The end bell 9 at one end of the armature has an orifice 15 throughwhich the fluid 16 may enter the armature cylindrical chamber 10. Thefluid 16 flows longitudinally within chamber 10 to the other end of thearmature where the fluid exits chamber 10 through orifice 17 and entersthe outer chamber 11. In passing through chamber 10 the fluid 16 bothcools and insulates the armature winding end turns 18 and the activeregion of the armature winding 2. The fluid l6 flows in the oppositelongitudinal direction in the outer chamber 11 where it cools the ironshield 14 and for the eddy current shield 12. Fluid 16 exits fromchamber 11 through orifice 19 in end closure I3. The flow of fluid 16through chambers 10, 11 is shown by direction arrows 20. Orifices 15, 19are connected to an oil pump 21 and oil cooler 22 which connectioncompletes the oil circulation loop.

External electrical connection to the armature winding is made bypassing the wire 23 of the end of a phase winding through a bushing 24which is capable of withstanding the phase voltage and the oil pressureof chamber 10, 11.

A cross sectional view of a section of the armature winding in thecentral portion of the armature is shown in FIG. 2. The outer tube 3surrounding the armature comprises a filament-wound glass-epoxy torquetube 25 under which there is a circumferentially wound glassfilament-epoxy shell 26. Tubes 25, 26 absorb the radial and torqueforces exerted on the armature winding when it is providing current. Twolayers of conductor bars 27 are shown to be separated by a shell 28which is of the same construction as shell 26. The conductor bars 27 ina layer of bars are spearated from one another by phenolic spacers 29.From FIG. 2, a cross sectional view perpendicular to the longitudinalaxis of the armature winding, it is seen than any unfilled region 30between the bars 27 and the outer tube 3 or the inner tube 4 willprovide a path for the axial flow of the oil through the armature. It isobserved that unfilled spaces 31 between the conductors 32 of a bar alsopro vide a path for oil flow. In addition, the conductors 32 maythemselves be formed of twisted strands of wire which will allow oilflow in the space between the twisted wires.

Where the armature conductors and bars are constructed so that thenaturally occurring passages for the flow of the cooling fluid asdescribed in the preceding paragraph are not large enough to adequatelycool the armature, as would be the case if the armature conductors 32were of square cross-section, the armature bars 27 may be modified bysubstituting tubing 33 for one or more of the conductors 32. The tubes33 would be of the same size as the conductors 32 and would be twistedalong with the conductors 32 to form the bar 27. The end-turnconnections of the bars would be made in a conventional manner whileexercising care to have the tube 33 ends open to fluid contained at eachend of chamber 10.

Although the invention has been described in terms of a preferredembodiment of an armature especially suited for use with a cryogenicfield winding, it is apparent that the invention need not be limited tothis form of armature. In particular a conventional armature capable ofproducing a sufficiently high voltage to result in a corona andflashover problem may be modified in accordance with this invention.Enclosing the conventional armature winding, including its end turns, ina fluid tight cylindrical enclosure and pumping oil into one end of theenclosure to cause oil flow through the conventional hollow armaturebars to the other end of the enclosure would produce the desiredinsulating effect on the armature end winding in addition to cooling thearmature.

Transformer oil would be a suitable fluid to provide the insulating andcooling function desired of the fluid in this invention. However, thereexist many other substances in either the gaseous or liquid form wellknown to those skilled in the art which would provide a suitable fluid.As an example, a material used for insulating pressurized transmissionlines, namely sulfahexafluoride, is believed suitable if the fluidchambers are designed to withstand the pressure at which thesulfahexafluoride would be used.

Although the invention has been described with particular reference tospecific embodiments, these are to be construed as illustrative only andnot as limitations on its scope and spirit which includes variations andmodifications within the capabilities of those skilled in the coolingand insulating arts.

What is claimed is:

1. A high voltage electrical machine comprising an armature winding,

a rotor within said armature winding,

a liquid-tight chamber completely surrounding said armature winding butexcluding said rotor,

said chamber having a cylindrical configuration at least in that portionof said chamber interposed between the armature and the rotor,

a fluid contained within and filling said chamber and in contact withthe armature winding,

said fluid being electrically insulating and cooling means forcirculating said fluid within said chamber,

the fluid flow within said chamber flows over the external and/orinternal regions of the armature bars of the winding including theend-turn region of the armature winding,

means for cooling said fluid in a closed system,

whereby the armature is cooled and insulated separately from the rotor.

2. The apparatus of claim 1 wherein said fluid is comprised oftransformer oil.

3. The apparatus of claim 1 wherein the fluid in contact with thearmature winding flows along, across, and 35 over the surface of barswhich comprise the armature winding.

4. The apparatus of claim 1 wherein, the armature winding is comprisedof bars having a passage for the flow of fluid along and through thelength of the bars which comprise the armature winding.

5. The apparatus of claim 5 wherein,

said bar comprises twisted circular conductors and the passage for theflow of fluid comprises the space between the conductors.

6. The apparatus of claim 6 wherein,

said circular conductors comprise twisted strands of wire having a spacebetween the strands to provide additional passages for the flow of fluidthrough the armature bar.

7. The apparatus of claim 1 wherein said bar comprises,

a plurality of electrical conductors, each of the same cross section,

at least one tube of the same cross sectional outline, said conductorsand tube being twisted around each other along their lengths toprovide'the conductor bar, the tube comprising the passage for the flowof fluid through and along the length of the bar.

8. The apparatus of claim 1 comprising in addition a second chamberconnected to the armature chamber by at least one fluid channel,

the second enclosure incorporating a flux shield to be cooled,

said fluid circulating means comprising a fluid pump and a fluid cooler,

each enclosure having an orifice to which the pump and cooler areserially connected to allow fluid flow through each enclosure.

9. The apparatus of claim 1 wherein said rotor comprises a cryogenicallycooled winding within a cylinder 5 containing the cryogenic fluid,

and said rotor cylinder and said armature cylinder superconducting.

1. A high voltage electrical machine comprising an armature winding, arotor within said armature winding, a liquid-tight chamber completelysurrounding said armature winding but excluding said rotor, said chamberhaving a cylindrical configuration at least in that portion of saidchamber interposed between the armature and the rotor, a fluid containeDwithin and filling said chamber and in contact with the armaturewinding, said fluid being electrically insulating and cooling fluid,means for circulating said fluid within said chamber, the fluid flowwithin said chamber flows over the external and/or internal regions ofthe armature bars of the winding including the end-turn region of thearmature winding, means for cooling said fluid in a closed system,whereby the armature is cooled and insulated separately from the rotor.2. The apparatus of claim 1 wherein said fluid is comprised oftransformer oil.
 3. The apparatus of claim 1 wherein the fluid incontact with the armature winding flows along, across, and over thesurface of bars which comprise the armature winding.
 4. The apparatus ofclaim 1 wherein, the armature winding is comprised of bars having apassage for the flow of fluid along and through the length of the barswhich comprise the armature winding.
 5. The apparatus of claim 5wherein, said bar comprises twisted circular conductors and the passagefor the flow of fluid comprises the space between the conductors.
 6. Theapparatus of claim 6 wherein, said circular conductors comprise twistedstrands of wire having a space between the strands to provide additionalpassages for the flow of fluid through the armature bar.
 7. Theapparatus of claim 1 wherein said bar comprises, a plurality ofelectrical conductors, each of the same cross section, at least one tubeof the same cross sectional outline, said conductors and tube beingtwisted around each other along their lengths to provide the conductorbar, the tube comprising the passage for the flow of fluid through andalong the length of the bar.
 8. The apparatus of claim 1 comprising inaddition a second chamber connected to the armature chamber by at leastone fluid channel, the second enclosure incorporating a flux shield tobe cooled, said fluid circulating means comprising a fluid pump and afluid cooler, each enclosure having an orifice to which the pump andcooler are serially connected to allow fluid flow through eachenclosure.
 9. The apparatus of claim 1 wherein said rotor comprises acryogenically cooled winding within a cylinder containing the cryogenicfluid, and said rotor cylinder and said armature cylinder beingseparated by a vacuum space.
 10. The apparatus of claim 4 wherein saidrotor comprises a winding of superconductors and said cryogenic fluid isat a temperature at which said rotor winding is superconducting.